$\dfrac{6}{8} - \dfrac{1}{12} = {?}$
$ = {\dfrac{6 \times 3}{8 \times 3}} - {\dfrac{1 \times 2}{12 \times 2}} $ $ = {\dfrac{18}{24}} - {\dfrac{2}{24}} $ $ = \dfrac{{18} - {2}}{24} $ $ = \dfrac{16}{24}$